1. Field of the Invention
The present invention relates generally to storage systems, and more particularly to disk drive servo controllers.
2. Background
Conventional computer systems typically include several functional components. These components may include a central processing unit (CPU), main memory, input/output (“I/O”) devices, and disk drives. In conventional systems, the main memory is coupled to the CPU via a system bus or a local memory bus. The main memory is used to provide the CPU access to data and/or program information that is stored in main memory at execution time. Typically, the main memory is composed of random access memory (RAM) circuits. A computer system with the CPU and main memory is often referred to as a host system.
The main memory is typically smaller than disk drives and may be volatile. Programming data is often stored on the disk drive and read into main memory as needed. The disk drives are coupled to the host system via a disk controller that handles complex details of interfacing the disk drives to the host system. Communications between the host system and the disk controller is usually provided using one of a variety of standard I/O bus interfaces.
Typically, a disk drive includes one or more magnetic disks. Each disk (or platter) typically has a number of concentric rings or tracks (platter) on which data is stored. The tracks themselves may be divided into sectors, which are the smallest accessible data units. A positioning head above the appropriate track accesses a sector. An index pulse typically identifies the first sector of a track. The start of each sector is identified with a sector pulse. Typically, the disk drive waits until a desired sector rotates beneath the head before proceeding with a read or writes operation. Data is accessed serially, one bit at a time and typically, each disk has its own read/write head.
FIG. 1 shows a disk drive system 100 with platters 101A and 101B, an actuator 102 and read/write head 103. Typically, multiple platters/read and write heads are used. Platters 101A–101B have assigned tracks for storing system information, servo data and user data.
The disk drive is connected to the disk controller that performs numerous functions, for example, converting digital to analog data signals, disk formatting, error checking and fixing, logical to physical address mapping and data buffering. To perform the various functions for transferring data, the disk controller includes numerous components.
To access data from a disk drive (or to write data), the host system must know where to read (or write data to) the data from the disk drive. A driver typically performs this task. Once the disk drive address is known, the address is translated to cylinder, head and sector, based on platter geometry and sent to the disk controller. Logic on the hard disk looks at the number of cylinders requested. Servo controller firmware instructs motor control hardware to move read/write heads 103 to the appropriate track. When the head is in the correct position, it reads the data from the correct track.
Typically, read and write head 103 has a write core for writing data in a data region, and a read core for magnetically detecting the data written in the data region of a track and a servo pattern recorded on a servo region.
A servo system 104 detects the position of head 103 on platter 101A according to the phase of a servo pattern detected by the read core of head 103. Servo system 104 then moves head 103 to the target position.
Servo system 104 servo-controls head 103 while receiving feedback for a detected position obtained from a servo pattern so that any positional error between the detected position and the target position is negated.
Typically, a servo controller in system 104 communicates with a data recovery device. One such device is shown in FIG. 3, as the “read channel device 303”. An example of such a product is “88C7500 Integrated Read channel” device sold by Marvell Semiconductor Inc®.
Typically, servo information is recorded in fixed amounts for a given product. In conventional systems, all the elements of servo fields are “hard-wired” to include details of interface timing between the servo controller and the read channel device 303. The conventional approach has drawbacks. For example, the servo controller design must be modified each time the format of any of the servo data elements changes. Also, if the interface between the read channel device 303 and servo controller (303A, FIG. 4) changes, the servo controller must be modified.
Therefore, what is desired is an efficient controller that can accommodate multiple interfaces and also future changes in servo field formats.